This invention relates to novel liquid crystal compounds and liquid crystal compositions containing the same.
Display elements utilizing liquid crystals have been broadly used for watches, electric calculators, etc. These liquid crystal display elements utilize the optical anisotropy and dielectric anisotropy of liquid crystal substances, and the liquid crystal phases include nematic liquid crystal phase, smectic liquid crystal phase and cholesteric liquid crystal phase. However, among these, display elements utilizing nematic liquid crystals have been most broadly practically used. Namely, correspondingly to the electro-optical effect which has been applied to liquid crystal display, display elements are classified into TN (twisted nematic) type, DS (dynamic scattering) type, guest-host type, DAP type, etc., and there vary properties required for liquid crystal substances used for these respective display elements. As for such liquid crystal substances, those which exhibit liquid crystal phases within a temperature range as broad as possible in the natural world are preferable. However, it is the present status that there is no substance which alone satisfies the above conditions, but several kinds of liquid crystal substances are mixed with one another or with non-liquid crystal substances, for practical use. The above substances are required to be stable to moisture, heat, air, etc.
Recently liquid crystal display elements capable of being driven under low voltage have been particularly required, and in order to satisfy such a requirement, a liquid crystal composition having a large value of dielectric anisotropy (hereinafter abbreviated to .DELTA..epsilon.) is usually required.
In general, a liquid crystal composition having an optional .DELTA..epsilon. value is obtained by adequately blending a compound of a positive .DELTA..epsilon. value with that of a negative .DELTA..epsilon. value. Thus in order to obtain a liquid crystal composition of a large .DELTA..epsilon. value, a component having as large a .DELTA..epsilon. value as possible may be used, and in that case, such a component should be a compound which has a good compatibility with other components and broadens or at least does not narrow the mesomorphic range of the resulting composition.
On the other hand, by using a liquid crystal composition having a large value of optical anisotropy (hereinafter abbreviated to .DELTA.n), it is possible to inhibit occurrence of color unevenness due to partially uneven distance between substrates of liquid crystal cell and to reduce the distance between the substrates; the reduced cell distance results for the composition in an advantage of increase in the intensity of electric field even under the same impressed voltage. Thus a compound which increases a .DELTA.n value of the resulting composition has been required.